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How accurate is an LCD screen version of the Pelli-Robson test?
Fabrizio Zeri1, Paolo Calcatelli2, Eleonora Funaro3
1Ophthalmic Research Group, School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK. f.zeri@aston.ac.uk.
Purpose:
To evaluate the accuracy and repeatability of a computer-generated Pelli-Robson test displayed on liquid crystal display (LCD) systems compared to a standard Pelli-Robson chart.
Methods:
Two different randomized crossover experiments were carried out for two different LCD systems for 32 subjects: 6 females and 10 males (40.5 ± 13.0 years) and 9 females and 7 males (27.8 ± 12.2 years), respectively, in the first and second experiment. Two repeated measurements were taken with the printed Pelli-Robson test and with the LCDs at 1 and 3 m. To test LCD reliability, measurements were repeated after 1 week.
Results:
In Experiment 1, contrast sensitivity (CS) measured with LCD1 resulted significantly higher than Pelli-Robson both at 1 and at 3 m of about 0.20 log 1/C in both eyes (p < 0.01). Bland-Altman plots showed a proportional bias for LCD1 measures. LCD1 measurements showed reasonable repeatability: ICC was 0.83 and 0.65 at 1 and 3 m, respectively. In Experiment 2, CS measured with LCD2 resulted significantly lower than Pelli-Robson both at 1 and at 3 m of about 0.10 log 1/C in both eyes (p < 0.01). Bland-Altman plots did not show any proportional bias for LCD2 measures. LCD2 measurements showed sufficient repeatability: ICC resulted 0.51 and 0.65 at 1 and 3 m, respectively.
Conclusions:
Computer-generated versions of Pelli-Robson test, displayed on LCD systems, do not provide accurate results compared to classic Pelli-Robson printed version. Clinicians should consider that Pelli-Robson computer-generated versions could be non-interchangeable to the printed version.
